What Are Ball Valves and Their Types?
Some of the most effective valves out there are also the simplest, and ball valves are no exception. Featuring a ball with a hole running through it, ball valves are able to control the flow of liquids, gasses, and vapors in a piping system with a simple motion. Operating like a movable pathway, the ball can be turned either so that there is a clear passage running through it or a rounded blockage. This design offers a very easy way of controlling fluid flow in a system by obstructing, restricting, or giving free passage for material to pass through.
Major Parts of a Ball Valve
Ball valves are used in countless pipelines because of their simple, but dependable, design which features five parts: a valve housing, ball, shaft, bonnet, and seat.
- Valve Housing: All internal components of a ball valve are held inside the valve housing or body. Often made of rigid metal, thermoplastic, or thermoplastic-lined metal, the housing is built to protect the components of the valve, as well as to give access to the external control mechanism that rotates the ball.
- Ball: As the defining feature for valves of this type, the ball serves a very special purpose as a changeable passageway for fluid to move through. To accomplish this, every ball has a hole running through its center that serves as the flow opening during operations. Otherwise, the flow can be throttled by the solid side of the ball. To suit different applications, the ball itself may be solid or hollow to affect how quickly the fluid will pass through. A solid ball has a constant opening diameter that helps the fluid to flow at a constant velocity. Alternatively, a hollow ball has a hollow internal structure so that the space inside it allows more fluid to pass through the valve. However, the larger space also creates turbulence and high velocities. Depending on the application, it may be better to choose a solid ball for more constant flow speed or a hollow one for greater volume.
- Shaft: The shaft is the connection between the ball and the control mechanism that can be used to rotate it. Though the control mechanism may either be manually operated by a lever or handwheel, or automatically by an electric, pneumatic, or hydraulic actuator, the shaft largely remains the same between all. In addition to having a cylindrical shape, the shaft almost always comes with some form of O-rings or packing rings. This is because, as a part which connects the internal and external components, the shaft could otherwise create a space for leakage.
- Bonnet: The bonnet is an extension of the valve housing that contains and protects the shaft and its packing. It may either be welded or bolted to the valve body and is usually made of hard metal. Like the role of packing rings alongside the shaft, the bonnet is also used to cover an opening. However, in this case, the bonnet is used to block the space which would otherwise be left between the shaft and the external control mechanism.
- Seat: Serving as the “seat” for the ball, this component provides a seal between the ball and the body of the valve. Its major role is to prevent the rotation of the ball from wearing out the component and its surrounding pipe.
Types of Ball Valves
Ball valves come in many different types and may be classified according to their housing assembly, ball design, and bore profile.
- Housing Assembly: When defining ball valves by their different housing assembly types, there are one-piece ball valves, split body ball valves, and top entry ball valves. One-piece ball valves have a single-piece cast body that houses the internal components of the ball valve. This eliminates leakage of fluid from the valve and makes them the cheapest ball valves available. Nevertheless, for applications that may require frequent pipe maintenance, split body ball valves can be a better option. Having a housing divided into two or three pieces that are fitted together, they can be taken apart and more easily cleaned and serviced when compared to their single-piece counterparts. Finally, for an even more accessible alternative, there are top entry ball valves. As their name implies, the design of these valves allow easy access to the internal sections of the valve by removing the bonnet. This allows for in-line maintenance activities like dismantling, cleaning, and inspection to be carried out without removing the ball valve from the main pipe.
- Ball Design: Ball valves can also be categorized by their ball design, the main types being floating, trunnion, and vented. Of these, floating balls are the most common design for ball valves, and it includes a ball that is suspended inside the valve so that it is free to move in a lateral direction when the valve is in a closed position. Alternatively, there are trunnion ball valves wherein the ball is supported by an additional shaft at its bottom. A vented ball valve is constructed in the same way as a standard ball valve with similar operations, differing in that the vented ball has small orifices drilled into its side.
- Bore Profile: Ball valves can also be organized by their bore profile with some being of the full bore variety while others are reduced or segmented. Full bore valves have a bore diameter that is similar to the pipe diameter of an assembly so that flow resistance is very low. In contrast, reduced bore ball valves have a bore diameter that is smaller than the pipe diameter. The flow area for the fluid becomes narrower, meaning the velocity increases. Finally, there are segmented ball valves that have a v-shaped notch on their ball. A segmented ball valve provides good flow rate control which is based on ball rotation.
Conclusion
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